ICL 7.1: Eye & Retina Flashcards
what are the parts of the eye?
out side
1. cornea
- anterior chamber
- iris
- pupil
- lens
- retina
inner most
what is inside the anterior chamber of the eye?
aqueous humor
what is the fovea?
the part of the eye with the highest seeing acute
what is the macula?
the space between the superior and inferior retinal arcade (vasculature)
which muscles does CN 3 innervate?
- superior rectus
- inferior rectus
- medial rectus
- inferior oblique
- pupil sphincter (parasympathetic)
- levator palpebrae
which muscles does CN 4 innervate?
superior oblique
which muscles does CN 6 innervate?
lateral rectus
which nerve controls the afferent pathway involving the pupils?
CN 2 controls the pathway from your eyes TO your brain
so CN 2 is what brings the light information to the brain
which nerve controls the efferent pathway involving the pupils?
CN 3 controls the pathway from your brain TO the eye
so CN 3 is what controls the eye muscles to react to the light
is CN 3 responsible for pupillary constriction or dilation?
constriction
it innervates the pupil sphincter!
pupillary constriction is controlled by the parasympathetic nervous system
what is the pupillary reaction to light?
if you shine a light in the left eye and everything is normal then the left pupil will constrict because CN 2 sent the information to the brain and then the brain sent information back to the eye via CN 3 to constrict the pupil
the right pupil will also constrict because of the consensual response!
what is an afferent pupillary defect?
if both eyes have an afferent pupillary defect and you shine light on the left eye, it won’t constrict because CN 2 is broken! glaucoma is the most common thing to damage CN 2 –> the right eye won’t constrict either because the afferent pathway is broken so there won’t be consensual constricting!
however, if there is an APD in the left eye but your right eye is okay and you shine light in the right eye, the right pupil will constrict AND and the left pupil will also constrict due to consensual response because even though the left afferents are broken, it’s efferents still work!
what is anisocoria?
this means the the pupils are different sizes
if you have an APD only in one eye, you WON’T have anisicoria because your efferent fibers are still working so you will have a consensual response that will still cause the broken eye to constrict
however, a condition that can cause one pupil to be smaller than the other is Horner syndrome which knocks out the sympathetic system and allows for uncontrolled parasympathetic responses which constrict your pupils!
which nerves control each of the muscles of the eye?
CN 3 controls the superior rectus, medial rectus, inferior rectus and inferior oblique
CN 4 controls the superior oblique
CN 6 controls the lateral rectus
which muscles of the eye will be spared in a retrobulbar block?
if you inject anesthetic into the muscular cone, the superior oblique will be the only functional eye muscle because CN 4 is outside the annulus of zenn so your eye will deviate down and out
CN 2, 3 and 6 are inside the annulus of zenn and also the nasociliary nerve (V1) and ophthalmic artery
CN 4, the superior opthalmic vein, frontal nerve and lacrimal nerve are all outside the annulus of zenn but inside the superior orbital fissure
which nerve is effected if a patient is unable to open their eyelid?
CN 3
CN 3 controls the levator palpebrae which opens your eye!
the other muscle responsible for opening the eye is the tarsal muscle which is sympathetically controlled so it’s not related to a CN and only does a few mm of eyelid opening –> so people with Horner’s syndrome who have knocked out their sympathetic nervous system will just have a mild ptosis since that knocks out the tarsal muscle but the levator palpebrae still works which does the majority of eye opening
how does CN 4 exit the brain?
it exits DORSALLY from the brainstem and travels around to the front to the eyeball so it has the longest intracranial course and is really susceptible to trauma!
CN 4 decussates as it exits the brain stem
note: it is the only cranial nerve to exit dorsally
what does a left-sided trochlear nerve palsy look like?
CN 4 = trochlear nerve
if CN 4 is knocked out then the superior oblique is knocked out and the left inferior oblique would be unopposed
this means the eye will be pointed up and out